Although Mac users don't garner nearly as many users as Windows does, 1 in 5 Mac users being left in the dust by Apple is nothing to sneeze at as noted in the Mac Virus blog by David Harley Senior Research Fellow at ESET working with the Cyber Threat Analysis Center since 2011:

Apple is not providing security updates for this OS? Where is the outrage?
rhetorical question really, all though usage could be as high 20% of Apple desktop OS users, the amount of people is a rounding error in XP users.
But this should throw cold water on generic claims that Apple desktop OS is more secure than other OS's.

Of all tyrannies, a tyranny sincerely exercised for the good of its victims may be the most oppressive. It would be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated; but those who torment us for our own good will torment us without end for they do so with the approval of their own conscience. ~C. S. Lewis

Apple is not providing security updates for this OS? Where is the outrage?

The equivalent OS to Snow Leopard is probably Vista, when it comes down to time frame. I have an older Mac that runs Tiger. There are quite a few folks that are running OS9, though some have finally moved on from that.

Snow Leopard is still popular, but just like XP.... it is time to move on. This OS is four generations ago. I think many systems running Snow Leopard could be moved to at least Lion.

Fact of the matter is there are fewer security issues with OSX than Windows. We have patches occasionally, but not nearly as often as with WIndows. Is that because of the smaller userbase? Probably not, but the core of OSX is unix-like, and it inherits many of the security benefits of the design.